The present disclosure generally relates to configurations, components, assemblies and methods for sealing cells of sodium-based thermal batteries, such as NaMx cells.
High-temperature rechargeable batteries, such as sodium-based thermal batteries like sodium metal halide or sodium sulfur cells, typically have a number of components that need to be sealed, such as hermitically sealed, for the cell to work. Sodium metal halide (NaMx) batteries, for instance, may include cells including a sodium metal anode and a metal halide (NiCl2 for example) cathode. A beta”-alumina solid electrolyte (BASE) separator can be used to separate the anode and cathode. The solid electrolyte may allow the transport of sodium ions between anode and cathode. A secondary electrolyte (NaAlCl4) can also used in the cathode mixture. The cathode mixture typically consists of nickel and sodium chloride along with other additives. The cathode mixture is contained inside the BASE tube, which is closed or sealed on one end after filling. At operating temperatures the cathode mixture may be in a molten fluid or fluid-like form.
In present typical designs of sodium-based thermal battery cells, such as NaMx cells and sodium-sulfur cells, the open end of the beta”-alumina ceramic tube is joined to an alpha-alumina collar using a glass seal. Spinel, zirconia, yttria, or other ceramic insulators, or combinations thereof, may also be used as a collar material in NaMx cells. The alpha-alumina collar isolates electrically the anode from the cathode. In order to enable the sealing of this ceramic subassembly to the current collectors (anode and cathode), and thereby at least partially seal the cell, two metallic rings (typically Ni) are typically coupled or bonded to the alpha-alumina collar prior to the sealing glass operation. The inside Ni ring is then typically welded to a cathode current collector assembly, and the current collector assembly includes another weld. The outside Ni ring is typically welded to an anode current collector (e.g., the metallic battery case) via a metal (e.g., Ni) outer bridge member. The integrity (e.g., strength and/or hermeticity) of the glass seal joint between the beta”-alumina ceramic tube and the alpha-alumina collar, the weld between the inside metal ring and the cathode current collector, the weld within the cathode current collector assembly, the welds between the bridge member and the outer metal ring and the anode current collector (e.g., the battery case), and the metal-ceramic joints between the outer and inner metal rings and the ceramic collar are all critical for the function, reliability and safety of the cell. As a result, each joint or seal must be performed under particular conditions and process steps particular to the specific type of seal (weld, glass seal, metallization/thermal compression bonding (TCB), etc.) being used to ensure sealing (e.g., hermeticity). Further, each seal must be inspected and/or tested. The relatively large amount of seals or joints also inherently provides a relatively large number of failure points. Such prior sealing configurations or processes are thereby disadvantageous as they are time consuming, costly and include numerous potential failure points.
There continues to be a growing need in the art for high performance sodium-based batteries with lower fabrication costs and high reliability. Thus, sealing configurations, systems and methods that are capable of achieving typical sodium-based battery performance and reduce fabrication time, costs and potential failure points are desirable.